[3/4] libcpp: Honour a configuration without host support for PCH.

diff --git a/libcpp/configure.ac b/libcpp/configure.ac
index 1efa96f7ca3..0533655e15a 100644
--- a/libcpp/configure.ac
+++ b/libcpp/configure.ac
@@ -183,6 +183,22 @@  if test x$ac_valgrind_checking != x ; then
  possible memory leaks because of libcpp use of interior pointers.])
 fi
 
+# The current default is that PCH is supported by the host unless otherwise
+# stated.
+AC_ARG_ENABLE(host_pch_support,
+AS_HELP_STRING([--disable-host-pch-support],
+	       [Disable host support for precompiled headers]),
+host_pch_support=$enableval,
+host_pch_support=yes)
+AC_SUBST(host_pch_support)
+HOST_PCH_SUPPORT=0
+if test x"$host_pch_support" != xno; then
+  AC_DEFINE(ENABLE_HOST_PCH_SUPPORT, 1,
+	    [Define this to 1 to enable support for precompiled headers.])
+else
+  AC_DEFINE(ENABLE_HOST_PCH_SUPPORT, 0)
+fi
+
 AC_ARG_ENABLE(canonical-system-headers,
 [  --enable-canonical-system-headers
                           enable or disable system headers canonicalization],
diff --git a/libcpp/files.c b/libcpp/files.c
index c93a03c69ef..800744b6a48 100644
--- a/libcpp/files.c
+++ b/libcpp/files.c
@@ -168,8 +168,10 @@  struct file_hash_entry_pool
 };
 
 static bool open_file (_cpp_file *file);
+#if ENABLE_HOST_PCH_SUPPORT
 static bool pch_open_file (cpp_reader *pfile, _cpp_file *file,
 			   bool *invalid_pch);
+#endif
 static bool find_file_in_dir (cpp_reader *pfile, _cpp_file *file,
 			      bool *invalid_pch, location_t loc);
 static bool read_file_guts (cpp_reader *pfile, _cpp_file *file,
@@ -195,7 +197,9 @@  static char *read_filename_string (int ch, FILE *f);
 static void read_name_map (cpp_dir *dir);
 static char *remap_filename (cpp_reader *pfile, _cpp_file *file);
 static char *append_file_to_dir (const char *fname, cpp_dir *dir);
+#if ENABLE_HOST_PCH_SUPPORT
 static bool validate_pch (cpp_reader *, _cpp_file *file, const char *pchname);
+#endif
 static int pchf_save_compare (const void *e1, const void *e2);
 static int pchf_compare (const void *d_p, const void *e_p);
 static bool check_file_against_entries (cpp_reader *, _cpp_file *, bool);
@@ -272,6 +276,7 @@  open_file (_cpp_file *file)
   return false;
 }
 
+#if ENABLE_HOST_PCH_SUPPORT
 /* Temporary PCH intercept of opening a file.  Try to find a PCH file
    based on FILE->name and FILE->dir, and test those found for
    validity using PFILE->cb.valid_pch.  Return true iff a valid file is
@@ -347,6 +352,7 @@  pch_open_file (cpp_reader *pfile, _cpp_file *file, bool *invalid_pch)
 
   return valid;
 }
+#endif
 
 /* Canonicalize the path to FILE.  Return the canonical form if it is
    shorter, otherwise return NULL.  This function does NOT free the
@@ -420,8 +426,14 @@  find_file_in_dir (cpp_reader *pfile, _cpp_file *file, bool *invalid_pch,
 	}
 
       file->path = path;
+#if ENABLE_HOST_PCH_SUPPORT
+      /* If there is no PCH this does not set the validity flag, so it keeps
+	 whatever value it had on entry.  */
       if (pch_open_file (pfile, file, invalid_pch))
 	return true;
+#else
+      *invalid_pch = false;
+#endif
 
       if (open_file (file))
 	return true;
@@ -1858,6 +1870,7 @@  remap_filename (cpp_reader *pfile, _cpp_file *file)
     }
 }
 
+#if ENABLE_HOST_PCH_SUPPORT
 /* Returns true if PCHNAME is a valid PCH file for FILE.  */
 static bool
 validate_pch (cpp_reader *pfile, _cpp_file *file, const char *pchname)
@@ -1889,6 +1902,7 @@  validate_pch (cpp_reader *pfile, _cpp_file *file, const char *pchname)
   file->path = saved_path;
   return valid;
 }
+#endif
 
 /* Get the path associated with the _cpp_file F.  The path includes
    the base name from the include directive and the directory it was
diff --git a/libcpp/pch.c b/libcpp/pch.c
index bb809641457..1dafcae6c4b 100644
--- a/libcpp/pch.c
+++ b/libcpp/pch.c
@@ -22,6 +22,7 @@  along with this program; see the file COPYING3.  If not see
 #include "hashtab.h"
 #include "mkdeps.h"
 
+#if ENABLE_HOST_PCH_SUPPORT
 static int write_macdef (cpp_reader *, cpp_hashnode *, void *);
 static int save_idents (cpp_reader *, cpp_hashnode *, void *);
 static hashval_t hashmem (const void *, size_t);
@@ -876,3 +877,14 @@  cpp_read_state (cpp_reader *r, const char *name, FILE *f,
   cpp_errno (r, CPP_DL_ERROR, "while reading precompiled header");
   return -1;
 }
+#else
+
+int cpp_save_state (cpp_reader *, FILE *) { return 0; }
+int cpp_write_pch_deps (cpp_reader *, FILE *) { return 0; }
+int cpp_write_pch_state (cpp_reader *, FILE *) { return 0; }
+int cpp_valid_state (cpp_reader *, const char *, int) { return 0; }
+void cpp_prepare_state (cpp_reader *, struct save_macro_data **) {}
+int cpp_read_state (cpp_reader *, const char *, FILE *,
+			   struct save_macro_data *) { return 0; }
+
+#endif